Method for transmitting response information in mobile communications system

ABSTRACT

A method for a user equipment (UE) to perform a random access to a network includes transmitting a random access preamble to the network; receiving control information via a downlink control channel from the network, wherein the control information includes downlink resource location information for a downlink shared channel and information for decoding the downlink shared channel; receiving a response to the random access preamble via the downlink shared channel from the network corresponding the control information, wherein the response has a variable size; and decoding the response based on the information for decoding the downlink shared channel.

TECHNICAL FIELD

Ii The present invention is directed to a mobile communication system,and, specifically to a method for transmitting response information in amobile communication system.

BACKGROUND ART

FIG. 1 is a structural diagram illustrating a Long Term Evolution (LTE)system which is a mobile communication system. The LTE system is anevolved version of a conventional UMTS system and has been standardizedby the 3GPP (3rd Generation Partnership Project).

The LTE network may be generally classified into an Evolved UMTSTerrestrial Radio Access Network (E-UTRAN) and a Core Network (CN). TheE-UTRAN includes at least one eNode-B serving as a base station and anAccess Gateway (AG) located at the end of the network so that it isconnected to an external network.

The AG may be classified into a portion for processing user traffic anda portion for processing control traffic. The AG portion for processinguser traffic and the AG portion for processing control traffic may beconnected to each other via a new interface for communication. One ormore cells may exist in an eNode-B. The eNode-Bs may be connected by aninterface for the transmission of user traffic or control traffic.

The CN includes the AG and a node for registering a user of the userequipment (UE). An interface may also be provided in the E-UMTS in orderto classify the E-UTRAN and the CN.

Radio interface protocol layers may be classified into the first layer(L1), the second layer (L2), and the third layer (L3) on the basis ofthree lower layers of an Open System Interconnection (OSI) referencemodel that is well known in the art. A physical layer of the first layer(L1) provides an information transfer service over a physical channel. Aradio resource control (RRC) layer located at the third layer (L3)controls radio resources between the UE and the network.

The RRC layer exchanges RRC messages between the UE and the network forthis purpose. The RRC layer may be distributed to a plurality of networknodes, such as eNode-B and AG, and may also be located at the eNode-B orthe AG.

FIG. 2 is a conceptual diagram illustrating a control plane of a radiointerface protocol structure between the UE and the UTRAN (UMTSTerrestrial Radio Access Network) based on the 3GPP radio access networkstandard. The radio interface protocol is horizontally represented by aphysical layer, a data link layer and a network layer. The radiointerface protocol is vertically represented by a user plane fortransmitting data and the control plane for transmitting controlsignals.

The protocol layers of FIG. 2 may be classified into a physical layer, aMedium Access Control (MAC) layer, a Radio Link Control (RLC) layer anda Radio Resource Control (RRC) layer.

The physical layer, which is a first layer, provides an informationtransfer service to an upper layer over a physical channel. The physicallayer is connected to a Medium Access Control (MAC) layer located thereabove via a transport channel.

The MAC layer communicates with the physical layer over the transportchannel such that data is communicated between the MAC layer and thephysical layer. Data is communicated among different physical layers,such as between a first physical layer of a transmission side and asecond physical layer of a reception side.

The MAC layer of the second layer (L2) transmits a variety of servicesto the RLC (Radio Link Control) layer, which is its upper layer, over alogical channel. The RLC layer of the second layer (L2) supportsreliable data transmission.

It should be noted that the RLC layer is depicted in dotted lines,because if the RLC functions are implemented in and performed by the MAClayer, the RLC layer itself may not need to exist.

The RRC (Radio Resource Control) layer located at the lowest portion ofthe third layer (L3) is defined by only the control plane. The RRC layercontrols logical channels, transport channels and physical channels forthe configuration, reconfiguration and release of Radio Bearers (RBs).An RB denotes a service provided by the second layer (L2) for datatransfer between the UE and the E-UTRAN.

FIG. 3 is a conceptual diagram illustrating a user plane of a radiointerface protocol structure between the UE and the UTRAN according tothe 3GPP radio access network standard. The radio protocol user planeclassifies into a physical layer, a MAC layer, a RLC layer and a PDCP(Packet Data Convergence Protocol) layer.

The physical layer of the first layer (L1) and the MAC and RLC layers ofthe second layer (L2) is used to effectively transmit data using an IPpacket, such as IPv4 or IPv6, on a radio interface with a relativelynarrow bandwidth. The PDCP layer performs header compression to reducethe size of a relatively-large IP packet header containing unnecessarycontrol information.

Uplink and downlink channels for transmitting data between the networkand the UE will hereinafter be described in detail. Downlink channelstransmit data from the network to the UE. Uplink channels transmit datafrom the UE to the network.

Examples of downlink channels are a Broadcast Channel (BCH) fortransmitting system information and a downlink Shared Channel (SCH) anda Shared Control Channel (SCCH) for transmitting user traffic or controlmessages. The use traffic or control messages of a downlink multicastservice or broadcast service may be transmitted over the downlink sharedchannel (SCH) or may be transmitted over an additional multicast channel(MCH).

Examples of uplink channels are a Random Access Channel (RACH) and anuplink shared channel (SCH) and a shared control channel (SCCH) fortransmitting user traffic or control messages.

FIG. 4 is a conceptual diagram illustrating a hybrid automatic repeatand request (HARQ) scheme. A method for implementing HARQ in thedownlink physical layer of a radio packet communication system will bedescribed with reference to FIG. 4.

Referring to FIG. 4, the eNode-B determines a UE that is to receivepackets and the type of packet that is to be transmitted to the UE, suchas a code rate, a modulation scheme and an amount of data. The eNode-Binforms the UE of the determined information over a High-Speed DownlinkShared Control Channel (HS-SCCH) and transmits a corresponding datapacket via High-Speed Downlink Shared Channel (HS-DSCH) at a timeassociated with the transmission of the information over the HS-SCCH.

The UE receives the downlink control channel, identifies a packet typeto be transmitted and a transmission time point, and receives thecorresponding packet. The UE then attempts to decode the received packetdata.

The UE transmits a negative acknowledgement (NACK) signal to the eNode-Bif the UE fails to decode a specific packet, such as data1. The eNode-Brecognizes that packet transmission has failed and re-transmits the samedata, such as data1, using the same packet format or a new packet formatat a suitable time point. The UE combines the re-transmitted packet,such as data1, and a previously received packet for which packetdecoding failed and re-attempts packet decoding.

The UE transmits an acknowledgement (ACK) signal to the eNode-B if thepacket is received and decoded successfully. The eNode-B recognizessuccessful packet transmission and performs transmission of the nextpacket, such as data2.

A random access channel (RACH) indicates a channel for transmitting aninitial control message from the UE to the network. The RACH is adaptedto implement synchronization between the UE and the network.Furthermore, if there is no more data for transmission left in a UE thatdesires to transmit data in an uplink direction, the UE can acquirenecessary radio resources over the RACH.

For example, when the UE is powered on it attempts to access a new cell.The UE performs downlink synchronization and receives system informationfrom a target cell desired by the UE.

Upon receiving the system information, the UE must transmit an accessrequest message to access the RRC layer. However, the UE is notsynchronized with a current network and there is no guarantee of uplinkradio resources since it uses the RACH.

In other words, the UE requests radio resources capable of transmittingthe access request message to the network. If the eNode-B receives theradio-resource request signal from the UE, it allocates suitable radioresources to the UE to transmit a RRC connection request message. The UEcan then transmit the RRC connection request message to the networkusing the allocated radio resources.

In another example, it is assumed that an RRC connection is establishedbetween the UE and the network. The UE receives radio resources from thenetwork according to the radio resource scheduling process of thenetwork such that data from the UE is transmitted to the network usingthe radio resources.

However, if there is no more data for transmission left in a buffer ofthe UE, the network no longer allocates uplink radio resources to theUE. If the network allocates the uplink radio resources to the UE, thisallocation is considered to be ineffective. The buffer state of the UE,is periodically or accidentally reported to the network.

Therefore, if new data is stored in the buffer of the UE having no radioresources, the UE utilizes the RACH since there are no uplink radioresources allocated to the UE. In other words, the UE requests radioresources required for data transmission to the network.

RACH as used in a Wideband Code Division Multiple Access (WCDMA) systemwill hereinafter be described in detail. The RACH is used fortransmission of data with short length. Some RRC messages, such as anRRC connection request message, a cell update message, and a URA updatemessage, are transmitted over the RACH.

A plurality of logic channels can be mapped to the RACH. For example, acommon control channel (CCCH), a dedicated control channel (DCCH), and adedicated traffic channel (DTCH) may be mapped to the RACH. The RACH ismapped to a physical random access channel (PRACH).

FIG. 5 is a conceptual diagram illustrating an example of a PRACH(Physical Random Access Channel) transmission method. As illustrated inFIG. 5, the PRACH which is an uplink physical channel is divided into apreamble part and a message part.

The preamble part performs a power-ramping function for adjusting powerrequired for transmitting a message and an anti-collision function forpreventing transmissions from several UEs from colliding with eachother. The message part performs transmission of a MAC Protocol DataUnit (MAC PDU) to the physical channel from the MAC layer.

If the MAC layer of the UE indicates the physical layer of the UE totransmit the PRACH transmission, the physical layer of the UE selects asingle access slot and a single signature and transmits the PRACHpreamble in the uplink. The preamble can be transmitted during an accessslot period of 1.33 ms and selects a single signature from among 16signatures during an initial predetermined period of the access slotsuch that it can transmit the selected signature.

When the UE transmits the preamble, the eNode-B can transmit a responsesignal over an acquisition indicator channel (AICH) which is a downlinkphysical channel. The eNode-B transmits a positive response (ACK) ornegative response (NACK) to the UE using a response signal transmittedover the AICH.

Tithe UE receives an ACK response signal, it transmits the message part.If the UE receives a NACK response signal, the MAC layer of the UEindicates the physical layer of the UE to perform PRACH retransmissionafter a predetermined time. If the UE does not receive a response signalcorresponding to the transmitted preamble, it transmits a new preambleat a power level that is higher than that of a previous preamble by onelevel after a designated access slot.

Although the above-mentioned description has disclosed a response signalto the RACH preamble, it should be noted that the eNode-B can transmitdata or control signals to the UE. There are a variety of controlsignals transmitted from the eNode-B to the UE, such as downlinkscheduling information, uplink scheduling grant information, andresponse information associated with the UE s RACH preambletransmission.

DISCLOSURE OF INVENTION Technical Problem

According to the conventional art, when the UE transmits data over theRACH, it transmits the RACH preamble to the eNode-B and the eNode-Btransmits response information associated with the RACH preamble to theUE. However, if at least two UEs transmit their RACH preambles in orderto use the RACH at the same or similar time, the eNode-B must informeach of the two UEs regarding response information associated with therespective preambles, thereby requiring the allocation of radioresources for transmitting the response information to each UE andwasting radio resources.

Provided that the UE uses the HARQ scheme when transmitting data to theeNode-B using the radio resources allocated over the RACH, the eNode-Bpre-allocates not only first radio resources associated with initialtransmission data but also second radio resources associated withre-transmission data. Therefore, the second radio resources for there-transmission data are unnecessarily wasted if the UE successfullytransmits data at a first transmission time.

Technical Solution

An object of the present invention is to provide a method fortransmitting response information in a mobile communication system thatreduces an amount of wasted radio resources and effectively uses radioresources. Another object of the present invention is to provide amobile communication system which does not transmit response informationassociated with UEs separately when two or more UEs have transmittedRACH preambles at the same or similar time, but rather transmits RACHpreamble response information to a specific UE, configures theassociated response information in the form of a single data unit over acommon channel, and transmits the configured data unit to the specificUE.

In one aspect of the present invention, a method for transmitting aspecific preamble and receiving information in response to the specificpreamble in a mobile communication system is provided. The methodincludes transmitting the specific preamble over a random access channel(RACH), receiving response information over a common channel, theresponse information including at least one response and identificationinformation corresponding to the at least one response, the at least oneresponse corresponding to at least one preamble transmitted during aspecific time interval and processing the at least one response if theidentification information indicates that the at least one responsecorresponds to the specific preamble.

It is contemplated that the method further includes transmitting datausing radio resources allocated in the at least one response if theidentification information indicates that the at least one responsecorresponds to the specific preamble. It is further contemplated thatthe method further includes receiving a first message including anindication that the transmitted data was not properly received andretransmitting the data using newly allocated radio resources.

It is contemplated that the first message includes the newly allocatedradio resources. It is further contemplated that the method furtherincludes receiving a second message including the newly allocated radioresources. Preferably, the common channel is a downlink shared channel(DL-SCH).

In another aspect of the present invention, a method for transmitting apreamble and receiving information in response to the preamble in amobile communication system is provided. The method includes receivingat least one preamble over a random access channel (RACH) during aspecific time interval and transmitting response information over acommon channel, the response information including a responsecorresponding to the at least one preamble received during the specifictime interval and identification information identifying a mobilecommunication terminal from which the at least one preamble wasreceived,

It is contemplated that the method further includes allocating radioresources in the response, the radio resources associated withtransmitting data from the mobile communication terminal from which theat least one preamble was received. It is further contemplated that themethod further includes receiving data from the mobile communicationterminal from which the at least one preamble was received, the datatransmitted using the allocated radio resources, determining that thedata was not properly received, transmitting a first message includingadditional allocated radio resources associated with retransmitting thedata and receiving the data retransmitted using the radio resourcesallocated in the message.

It is contemplated that the method further includes including anindication in the first message that the data was not properly received.It is further contemplated that the method further includes transmittinga second message including an indication that the data was not properlyreceived. Preferably, the common channel is a downlink shared channel(DL-SCH).

In another aspect of the present invention, a method for transmitting aspecific preamble and receiving information in response to the specificpreamble in a mobile communication system is provided. The methodincludes a specific mobile communication terminal transmitting thespecific preamble over a random access channel (RACH), a networktransmitting response information over a common channel, the responseinformation including a response corresponding to at least one preamblereceived during a specific time interval and identification informationidentifying a mobile communication terminal from which the at least onepreamble was received, the specific mobile communication terminalreceiving the response information and the specific mobile communicationterminal processing the at least one response if the identificationinformation indicates that the at least one response corresponds to thespecific preamble.

It is contemplated that the method further includes the networkallocating radio resources in the response, the radio resourcesassociated with transmitting data from the mobile communication terminalfrom which the at least one preamble was received. It is furthercontemplated that the method further includes the specific mobilecommunication terminal transmitting data using the radio resourcesallocated in the at least one response if the identification informationindicates that the at least one response corresponds to the specificpreamble.

It is contemplated that the method further includes the networkreceiving data from the mobile communication terminal from which the atleast one preamble was received, the data transmitted using theallocated radio resources, the network determining that the data was notproperly received, the network transmitting a first message includingadditional allocated radio resources associated with retransmitting thedata, the specific mobile communication terminal retransmitting the datausing the radio resources allocated in the first message and the networkreceiving the data retransmitted using the radio resources allocated inthe message. It is further contemplated that the method further includesthe network including an indication in the first message that the datawas not properly received.

It is contemplated that the method further includes the networktransmitting a second message including an indication that the data wasnot properly received. It is further contemplated that the commonchannel is a downlink shared channel (DL-SCH).

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. It is to beunderstood that both the foregoing general description and the followingdetailed description of the present invention are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

These and other embodiments will also become readily apparent to thoseskilled in the art from the following detailed description of theembodiments having reference to the attached figures, the invention notbeing limited to any particular embodiments disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. Features, elements, and aspects of the invention that arereferenced by the same numerals in different figures represent the same,equivalent, or similar features, elements, or aspects in accordance withone or more embodiments.

FIG. 1 is a structural diagram illustrating a Long Term Evolution (LTE)system which is a mobile communication system.

FIG. 2 is a conceptual diagram illustrating each layer of a controlplane of radio interface protocols

FIG. 3 is a conceptual diagram illustrating each layer of a user planeof radio interface protocols.

FIG. 4 is a conceptual diagram illustrating a hybrid ARQ (HARQ) scheme.

FIG. 5 is a conceptual diagram illustrating an example of a PRACH(Physical Random Access Channel) transmission method.

FIG. 6 is a flow chart illustrating a method for transmitting responseinformation in a mobile communication system according to one embodimentof the present invention.

FIG. 7 is a conceptual diagram illustrating a method for transmittingresponse information to a UE over a common channel according to oneembodiment of the present invention.

FIG. 8 is a flow chart illustrating a method for transmitting responseinformation in a mobile communication system according to anotherembodiment of the present invention.

FIG. 9 is a flow chart illustrating a method for transmitting responseinformation in a mobile communication system according to anotherembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

A method for transmitting response information in a mobile communicationsystem according to the present invention will hereinafter be describedwith reference to the accompanying drawings. For the convenience ofdescription and better understanding of the present invention, the term“UE” will be used to indicate a transmission entity of an uplink signaland the term “eNode-B” will be used to indicate a reception entity ofthe uplink signal. However, it should be noted that the scope of theterminal and the base station is not limited to the above-mentionedterms and the term “UE” and the term “eNode-B” may also be used toindicate, respectively, a terminal and a base station.

FIG. 6 is a flow chart illustrating a method for transmitting responseinformation in a mobile communication system according to one embodimentof the present invention. A method for transmitting response informationassociated with preamble transmission of at least one UE at a time willhereinafter be described.

The UE uses the RACH to perform a RRC connection request, a cell update,a handover, an uplink radio resource request and maintenance ofsynchronization associated with the eNode-B. The UE transmits a preambleprior to the transmitting of data. The preamble uses for adjustingtransmission power required for data transmission and for preventingseveral UEs from colliding with each other.

When using RACH, the UE transmits the RACH preamble to the eNode-B andthe eNode-B transmits RACH preamble response information to the UE. TheeNode-B does not independently transmit response information associatedwith other UEs, each of which transmits RACH preambles at the same orsimilar time, but rather transmits the response information associatedwith the other UEs over a common channel at the same time.

For example, if a first UE, a second UE, and a third UE transmit theirRACH preambles to the eNode-B within a predetermined period of time, theeNode-B configures response information associated with the firstthrough third UEs in the form of a single data unit and transmits thesingle data unit to the first through third UEs over a common channel inorder to reply to the RACH preambles of the first through third UEs.

As illustrated in FIG. 6, the first UE (UE1) transmits its RACH preambleto the eNode-B at step S60 and the second UE (UE2) transmits its RACHpreamble to the eNode-B at the same time or a similar time as the RACHpreamble of the first UE is transmitted. In other words, the first UE(UE1) and the second UE (UE2) transmit their RACH preambles to theeNode-B at the same or similar time.

Therefore, the eNode-B receives at least one RACH preamble from at leasttwo UEs during a predetermined time (Δ,). Although FIG. 6 illustratesonly the first (UE1) and second (UE2) UEs, it is obvious to thoseskilled in the art that the number of UEs may be N and the presentinvention may also be applied to N UEs.

The eNode-B receives RACH preambles of the first (UE1) and second (UE2)UEs and transmits response information of the received RACH preambles atstep S62. The eNode-B transmits the response information over a commonchannel without allocating unique radio frequency RF channels to thefirst (UE1) and second (UE2) UEs in order to reply to the RACHpreambles. The common channel allows all UEs within a cell to receive orread data from the eNode-B.

FIG. 7 is a conceptual diagram illustrating a method for transmittingresponse information to a UE over a downlink shared channel (DL-SCH)which is a common channel according to the one embodiment of the presentinvention. Generally, the DL-SCH is used to transmit data from theeNode-B to predetermined UEs or is used to transmit data to all UEs in acell. Therefore, different UEs may receive data over the DL-SCH.

Although the eNode-B simultaneously transmits response informationassociated with a plurality of UEs over the DL-SCH, each UE can receiveits response information from the eNode-B. The eNode-B transmitsresponse information associated with the RACH preambles to the UEs overthe DL-SCH. The single data unit of response information includes aplurality of response information associated with a plurality of UEs.

As illustrated in FIG. 7, the UE must first read the downlink sharedcontrol channel (DL-SCCH) in order to read data of the DL-SCH. Thelocation information of the DL SCH is transmitted over the DL-SCCH.

In other words, after transmitting the RACH preamble, the UE reads theDL-SCCH to receive response information from the eNode-B and thenrecognizes location information of the DL-SCH associated with theDL-SCCH. Control signals associated with the physical layer and/or thesecond layer are transmitted from the eNode-B to the UE over theDL-SCCH.

The DL-SCCH carries a variety of information, such as a UE ID(Identifier) for indicating which one of UEs will receive the data,location information related to frequency or time that indicates whichDL-SCH data will be read by the UEs, specific information required byUEs that desire to read the DL-SCH data, and decoding information. Inthis way, it can be recognized which one of UEs will receive specificDL-SCH data by means of the UE ID included in DL-SCCH.

As illustrated in FIG. 6, the DL-SCH carries first response informationfor the first UE (UE1) and second response information for the second UE(UE2). In other words, the first UE (UE1) and the second UE (UE2) readthe same DL-SCCH and determine the same DL-SCH location.

The first UE (UE1) and the second UE (UE2) read their unique responseinformation over the same DL-SCH. The response information of the RACHpreambles transmitted from the UEs at the same or similar time transmitsto the UEs by multiplexing each response information for each UE at thesecond layer of the eNode-B.

The eNode-B configures the response information of the RACH preambleshaving been transmitted by the UEs at the same or similar time. Theresponse information is configured in the form of a single MAC ProtocolData Unit (PDU).

A method for multiplexing the response information of the UEs toconfigure a single MAC PDU and transmitting the single MAC PDU willhereinafter be described with reference to Tables 1 and 2.

A representative example of a PDU configured by multiplexing of responseinformation is shown in Table 1:

TABLE 1 First UE′ First UE′ Second Second . . . N-thUE′ N-th UE′ headerresponse UE′ UE′ header response information header response infor-information mation

As illustrated in Table 1, the eNode-B configures a first UE′ headerprior to the first UE′ response information. The header includes a UE IDindicating for which UE the response information is intended to read andalso includes specific information indicating the length of the responseinformation.

The eNode-B configures the first UE′ response information after thefirst UE header. The response information for the first UE includesuplink radio resources allocated to the first UE, an identifier within acell, a temporary identifier of the first UE, and a compensation valueassociated with synchronization with the eNode-B.

After configuring the first UE header and the first UE′ responseinformation, the eNode-B configures the second UE′ header and the secondUE′ response information. In this way, the PDU generated by includingresponse information of several UEs in single response information maybe configured.

Another example of a single PDU configured by the multiplexing ofresponse information is shown in Table 2.

As illustrated in Table 2, a header including the first UE′ identifierand the length of response information is attached to the MAC PDU. Theheader serves the same function as that of the header illustrated in theTable 1.

TABLE 2 First Second . . . N-thUE′ Indicator First UE′ Second UE′ . . .N-th UE′ UE′ UE′ header header response response response header headerend information information information

The second UE′ header is the attached to the PDU after the first UE′header. In this way, the PDU includes as many headers as the number (N)of UEs for which response information is to be included in singleresponse information.

An indication indicating the end of the header is attached to the end ofthe header. The eNode-B can recognize the beginning of the responseinformation using this header. Thereafter, the MAC PDU is formed bysequentially attaching response information of individual UEs.

The response information of each UE includes information of uplink radioresources allocated to the each UE, an identifier within a cell, atemporary identifier of the UE, and a compensation value associated withsynchronization a with the eNode-B. Each UE recognizes its own responseinformation from among a plurality of response information that havebeen multiplexed into the single response information and transmittedover the common channel. Each UE transmits data to the eNode-B usinguplink radio resources allocated to the each UE in the responseinformation associated with its RACH preamble.

FIG. 8 is a flow chart illustrating a method for transmitting responseinformation in a mobile communication system according to anotherembodiment of the present invention. Specifically, FIG. 8 illustrates ascheduling method for a specific case in which a HARQ (Hybrid ARQ)scheme is used when data is transmitted to the eNode-B.

As illustrated in FIG. 8, a first UE (UE1) transmits its RACH preambleto the eNode-B at step S70 and a second UE (UE2) transmits its RACHpreamble to the eNode-B at step S71 in a manner similar to thatillustrated in FIG. 6. The first UE (UE1) and second UE (UE2) receiveresponse information configured in the form of a single data unit over acommon channel, such as a DL-SCH, at step S72.

Each UE then transmits data to the eNode-B using uplink radio resourcesallocated to the each UE in the response information associated witheach RACH preamble. It should be noted that FIG. 8 illustrates only adata transmission/reception process between the second UE (UE2) and theeNode-B after reception of the response information. It is obvious tothose skilled in the art that the above-mentioned process can also beapplied to the case of the first UE (UE1) in the same manner as for thesecond UE (UE2).

Provided that the HARQ scheme is used when each UE transmits data to theeNode-B using the uplink radio resources allocated over the RACH, uplinkradio resources for data re-transmission are not pre-allocated butrather allocated and transmitted to each UE with a NACK signal when datare-transmission is required due to a decoding failure of the eNode-B.The uplink radio resources for data retransmission may be included inthe NACK signal. A specific control signal may be used to allocate theuplink radio resources for re-transmission to the UE.

As illustrated in FIG. 8, the second UE (UE2) transmits data to theeNode-B at step S73 after receiving the response information from theeNode-B. The second UE (UE2) employs a HARQ scheme when transmitting theabove-mentioned data to the eNode-B. The eNode-B informs the UEs of thesetup of the HARQ scheme through system information.

The eNode-B receives the data from the second UE (UE2) and decodes thereceived data. If the eNode-B does not decode the data correctly, ittransmits a NACK signal to the second UE (UE2) to indicate a decodingerror at step S74.

The eNode-B allocates radio resources required for data re-transmissionto the second UE (UE2), and transmits information associated with theallocated radio resources along with the NACK signal at the same time.In other words, the uplink radio resource allocation information in theresponse information is related only to the first transmission of theHARQ when the eNode-B transmits response information of the RACHpreamble to the UE.

For example, if the radio resources required for data transmission afterthe RACH preamble have a specific value of 100 and the data requiresre-transmission due to the HARQ operation, the UE re-requires the radioresources of 100. If the data retransmission is applied to a case inwhich the eNode-B allocates uplink radio resources according to the UE sRACH preamble, radio resources of 200 will be allocated to the UE.

However, when allocating radio resources as response information of theUE s RACH preamble, the eNode-B allocates only the 100 radio resourcesassociated with the first transmission to the UE according to thepresent invention. Thereafter, if data re-transmission is required dueto failure of a UE s data transmission, the eNode-B additionallyallocates not only the NACK signal but also the 100 additional radioresources to the UE.

The specific control signal including the radio-resource allocationinformation required for data re-transmission may be transmittedaccording to the same format as that for the RACH preamble s responseinformation. Also, a channel used when the eNode-B allocates radioresources to the UE may also be used as an example of the presentinvention.

The second UE (UE2) re-transmits the data at step S75 according touplink radio resource allocation information that was transmitted withthe NACK signal.

FIG. 9 is a flow chart illustrating a method for transmitting responseinformation in a mobile communication system according to anotherembodiment of the present invention. Specifically, FIG. 9 illustrates ascheduling method for a specific case in which a HARQ (Hybrid ARQ)scheme is used when data is transmitted to the eNode-B. One ofdifferences with the case of FIG. 8 is that uplink radio resources fordata retransmission may not be included in the NACK signal but betransmitted separately with the NACK signal at the same or another time.

As illustrated in FIG. 9, a first UE (UE1) transmits its RACH preambleto the eNode-B at step S80 and a second UE (UE2) transmits its RACHpreamble to the eNode-B at step S81 in a manner similar to thatillustrated in FIG. 6 and FIG. 8. The first UE (UE1) and second UE (UE2)receive response information configured in the form of a single dataunit over a common channel, such as a DL-SCH, at step S82.

Each UE then transmits data to the eNode-B by using uplink radioresources allocated to the each UE in the response informationassociated with each RACH preamble at the step S83. It should be alsonoted that FIG. 9 illustrates only a data transmission/reception processbetween the second UE (UE2) and the eNode-B after reception of theresponse information. It is obvious to those skilled in the art that theabove-mentioned process can also be applied to the case of the first UE(UE1) in the same manner as for the second UE (UE2).

The second UE (UE2) employs a HARQ scheme when transmitting theabove-mentioned data to the eNode-B. The eNode-B preferably informs theUEs of the setup of the HARQ scheme through system information.

Provided that the HARQ scheme is used when each UE transmits data to theeNode-B by using the uplink radio resources allocated over the RACH,uplink radio resources for data re-transmission are not pre-allocatedbut rather allocated and transmitted to each UE with a NACK signal whendata re-transmission is required due to a decoding failure of theeNode-B. The NACK signal transmitted when data retransmission isrequired due to a decoding failure of the eNode-B at the step S84. Andthe uplink radio resources for data re-transmission are allocated.Namely, the uplink radio resources for data re-transmission are notpre-allocated but rather allocated and transmitted to each UE whenre-transmission is necessary. A specific control signal may be used toallocate the uplink radio resources for re-transmission to the UE. Thespecific control signal may be a signal for SR (Scheduling Resources)from the eNode-B at the step S85. The specific control signal may bealso a signal for scheduling information or any other signals.

The specific control signal including the radio resource allocationinformation required for data re-transmission may be transmittedaccording to the same format as that for the RACH preamble s responseinformation. Also, a channel used when the eNode-B allocates radioresources to the UE may also be used as an example of the presentinvention.

The second UE (UE2) re-transmits the data at step S86 according touplink radio resource allocation information that was transmitted withthe specific control signal for example, SR.

As described herein, the method for transmitting response information ina mobile communication system according to the present invention canmore effectively use radio resources, thereby reducing the amount ofwasted radio resources.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims. Therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are intended to beembraced by the appended claims.

INDUSTRIAL APPLICABILITY

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses.

The description of the present invention is intended to be illustrative,and not to limit the scope of the claims. Many alternatives,modifications, and variations will be apparent to those skilled in theart. In the claims, means-plus-function clauses are intended to coverthe structure described herein as performing the recited function andnot only structural equivalents but also equivalent structures.

1. A method for a user equipment (UE) to perform a random access to anetwork, the method comprising: transmitting a random access preamble tothe network; receiving control information via a downlink controlchannel from the network, wherein the control information comprisesdownlink resource location information for a downlink shared channel andinformation for decoding the downlink shared channel; receiving aresponse to the random access preamble via the downlink shared channelfrom the network corresponding the control information, wherein theresponse has a variable size; and decoding the response based on theinformation for decoding the downlink shared channel.
 2. The method ofclaim 1, wherein the information for decoding the downlink sharedchannel informs the UE of the variable size of the response.
 3. Themethod of claim 1, wherein the response comprises one or more randomaccess responses.
 4. The method of claim 3, further comprising:processing a specific random access response, when the specific randomaccess response among the random access responses corresponds to thetransmitted random access preamble.
 5. The method of claim 4, whereinthe specific random access response comprises an identifier of the UE, avariable for synchronization and uplink resource allocation information.6. The method of claim 5, further comprising: transmitting uplink datato the network based on the uplink resource allocation information whenthe response is decoded.
 7. The method of claim 1, wherein the UEcomprises a physical layer and a MAC (Medium Access Control) layer, andwherein the physical layer of the UE transmits the random accesspreamble to the network upon receiving an instruction from the MAClayer.
 8. A user equipment (UE) performing a random access to a network,the UE comprising: a transmitter configured to transmit a random accesspreamble to the network; a receiver configured to receive controlinformation via a downlink control channel from the network, wherein thecontrol information comprises downlink resource location information fora downlink shared channel and information for decoding the downlinkshared channel, and to receive a response to the random access preamblevia the downlink shared channel from the network corresponding to thecontrol information, wherein the response has a variable size; and adecoder configured to decode the response based on the information fordecoding the downlink shared channel.
 9. The UE of claim 8, wherein theinformation for decoding the downlink shared channel informs the UE ofthe variable size of the response.
 10. The UE of claim 8, wherein theresponse comprises one or more random access responses.
 11. The UE ofclaim 10, further comprising: a processor configured to process aspecific random access response, when the specific random accessresponse among the random access responses corresponds to thetransmitted random access preamble.
 12. The UE of claim 11, wherein thespecific random access response comprises an identifier of the UE, avariable for synchronization and uplink resource allocation information.13. The UE of claim 12, wherein the transmitter is further configured totransmit uplink data to the network based on the uplink resourceallocation information when the response is decoded.
 14. The UE of claim8, wherein the UE comprises a physical layer and a MAC (Medium AccessControl) layer, and wherein the physical layer of the UE transmits therandom access preamble to the network upon receiving an instruction fromthe MAC layer.
 15. A method for a network to control a random access ofa user equipment (UE), the method comprising: receiving a random accesspreamble from the UE; transmitting control information via a downlinkcontrol channel to the UE, wherein the control information comprisesdownlink resource location information for a downlink shared channel andinformation for decoding the downlink shared channel; and transmitting aresponse to the random access preamble via the downlink shared channelto the UE, wherein the response has a variable size corresponding to theinformation for decoding the downlink shared channel.
 16. The method ofclaim 15, wherein the information for decoding the downlink sharedchannel informs the UE of the variable size of the response.
 17. Themethod of claim 15, wherein the response comprises one or more randomaccess responses.
 18. The method of claim 17, wherein each of the randomaccess responses comprises an identifier of the UE, a variable forsynchronization and uplink resource allocation information.
 19. Anetwork for controlling a random access of a user equipment (UE), thenetwork comprising: a receiver configured to receive a random accesspreamble from the UE; and a transmitter configured to transmit controlinformation via a downlink control channel to the UE, wherein thecontrol information comprises downlink resource location information fora downlink shared channel and information for decoding the downlinkshared channel, and to transmit a response to the random access preamblevia the downlink shared channel to the UE, wherein the response has avariable size corresponding to the information for decoding the downlinkshared channel.
 20. The network of claim 19, wherein the information fordecoding the downlink shared channel informs the UE of the variable sizeof the response.
 21. The network of claim 19, wherein the responsecomprises one or more random access responses.
 22. The network of claim21, wherein each of the random access responses comprises an identifierof the UE, a variable for synchronization and uplink resource allocationinformation.